Grinding of contact lenses



Sept. 14, 1965 P. F. THOMAS 3,205,625

GRINDING OF CONTACT LENSES Filed Jan. 30, 1965 3 Sheets-Sheet l 33 4a |4o I o 32 o r 20 45 l'9 g o 0 Q: v i v I9 1'8 I6 23 L FIG! Sept. 14, 1965P. F. THOMAS 3,205,625

GRINDING 0F CONTACT LENSES Filed Jan. 30, 1965 3 Sheets-Sheet 2 p 1965P. F. THOMAS 3,205,625

ND '1 NSE United States Patent 3,205,625 GRINDING 0F tZONlACll LENSESPenrhyn Francis Thomas, Sydney, New South Wales,

Australia, assignor to Corneal Lens Corporation Pty. Limited, Sydney,New South Wales, Australia, a com pany of New South Wales, AustraliaFiled Jan. 30, 12163, Ser. No. 254,957

Claims priority, application Australia, Feb. 6, 1962,

4 Claims. (Cl. 51284) The invention relates to the grinding of contactlenses and more specifically to the grinding of the secondary curves onsuch lenses sometimes referred to as the limbal band.

Contact lenses, which are designed to fit on the cornea of the humaneye, consist generally of an inner part which constitutes the optic andis ground to the required power and an outer part, the limbal band,which is composed of a number of so-called secondary curves, of greaterradius than the optic and designed to fit the cornea of the wearer.

While the secondary curves are ground on the concave side of the lens itis also necessary to grind the convex side of the lens outside theactual optic to maintain a predetermined thickness of the lens on itsperiphery. In addition, the outer part has to be ground in such a waythat its centre plane forms a predetermined angle with a tangentialplane through the apex of the optic.

This angle is dependent, in the same way as the limbal band, on theshape of the cornea to which the lens is to be applied.

In the past grinding of the individual secondary curves was carried outby separate grinding operations and a further operation was required toshape the lens periphery.

This manufacturing method not only necessitates a substantial number ofindividual grinding operations, but makes it rather diflicult toreproduce exactly the same limbal band when grinding a plurality oflenses as minor variations in the individual grinding operations areunavoidable. Furthermore, sharp ridges will appear where two curves ofthe limbal band meet each other and these ridges have to be removed byfurther grinding.

The beforementioned disadvantages are overcome according to theinvention by a method for grinding lenses comprising the steps ofmounting the lens to be ground on a rotatable support, adjusting thesupport to bring the lens in contact with a grinding tool and moving thegrinding tool over the lens surface by means of a pantograph device andcontrolling the movement of the pantograph device from a templaterepresenting an enlarged replica of the periphery and thecross-sectional curves of the lens.

In one form of the invention the lens is positioned in a rotating holderin any known manner. The grinding tool support is fixed to the free armof a pantograph which is so arranged that the grinding head can passfrom one side of the lens periphery to the other side.

The guiding or tracer arm of the pantograph carries a tracer head whichis guided by a template giving an exact replica of a cross-sectionthrough the required outer part of the lens including the varioussecondary curves. The template can be made on a much larger scale thanthe actual lens curve, as the pantograph will automatically reduce themovement of the grinding head to any desired degree, thus a greataccuracy in grinding can be achieved. In one grinding operation theperiphery of the lens can be shaped and brought down to the requiredthickness and the various secondary curves forming the limbal band areground in the same operation. As the tracer pin moves from one curve tothe other without interruption any sharp ridges between adjoining curvesare eliminated.

3,25,6Z5 Patented Sept. 14, 1965 One embodiment of the invention isdescribed hereinafter in connection with the drawings in which:

FIGURE 1 shows a perspective view of the apparatus according to theinvention;

FIGURE 2 shows the tracer head, its mounting and part of the template ofFIGURE 1 on an enlarged scale;

FIGURE 3 shows the grinding head of FIGURE 1 and its mountings on anenlarged scale.

As shown in FIGURE 1 the apparatus has a base plate 1 which supports allthe various parts referred to hereinafter.

The concavo-convex lens to be ground is fitted on a lens holder 2secured in suitable manner in a shaft 3 supported by a head stock 4.Pulleys 5 are fixed on shaft 3 and are driven by a belt 6 from anelectric motor 7 mounted on a support 8 secured to the base 1. The headstock 4 is secured on a saddle 9 which slides on a vertical slide 10 andis adjustable in its position by means of a spindle 11. The slide 10forms part of a bracket 12, which in turn is adjustably mounted on thebracket slide 13 for hori- Zontal movement thereon by means of spindle14. The bracket slide 13 forms an integral part with a bed plate 15secured to the base plate 1.

A pantograph mechanism is rotatably supported on the base plate 1 by acolumn 16. This mechanism consists basically of two pairs of bars 17,18, the bars of each pair being spaced from each other by spacers 19. Onone side the end of the bar pairs are linked with each other by acrosspiece 20 rotatably connected thereto while the other ends of thebar pairs are rotatably linked by a guiding or tracer arm 21 whichcarries at its extended end the tracer head 22. To increase stabilitythe tracer arm 21 is guided over the base plate 1 by means of casters23.

The tracer head 22, which will be described in more detail later on, isguided, for example, manually along a template 24 representing therequired curves of the lens, and the template is clamped by a clampingdevice 25 to a horizontal table 26 which can carry the necessary scalesor graduations 27 for setting the template to the required position. Thetable 26 is movable in two directions at right angles to each other inrelation to the base plate 1 by means of spindles 28 and 29.

As mentioned above, the pantograph is rotatably mounted on the column16. A pivot on column 16 engages the pair of bars 17 at a point slightlyinwards from the linkage point 31 of bars 17 with the cross piece 20 asshown in FIGURE 3. In a practical example the pivot point is arrangedabout /2" from the ends of bars 17. The cross piece 20 is extendedbeyond the bars 17 as shown at 30 and the linkage point 31 is bridged bya bridge 32 which carries a disc 33 rotatably mounted thereon. Thecentre of the disc 33 is offset from the linkage point 31 in thedirection of extension 30 of cross piece 20. A tool holder 34 is fixedto the disc and a grinding head 35, for example, a diamond head, ismounted in the tool holder 34 in such a manner that its tip lies in thevertical axis through the centre of the disc and the grinding headitself swings around this axis on rotation of the disc.

If required a polishing bull 36 can also be mounted by means of bracket37 on the tool holder 34 so that its axis of rotation lies in thevertical axis through the disc centre. The butt 36 is driven, forexample, by a flexible shaft 38, from an electromotor 39 (FIGURE 1),suitably mounted on the support 8.

The disc 33 is connected by a linkage with the tracer head 22 to berotated thereby as will be described hereinafter. The tracer head 22 hasa shaft 40 with a knurled knob 41. Fixed to the shaft 40 is a lever 42,which is linked at its free end to a rod 43. The other end of rod 43 ispivoted at one arm of a bell crank lever 44 which is mounted on theextended end of the tracer arm 21. The other arm of the bell crank lever44 is linked with a rod 45 which in turn connects over the link 46 withthe disc 33. Thus any rotation of the shaft 40 will be transmitted overthe linkage to impart a corresponding angular movement of the disc 33with its toolholder 34.

The lower end of the shaft 40 is fixed in a mounting block 47 (FIGURE 2)which carries a guide roller 48 and a hookshaped extension or catch 49.The guide roller 48 is rotatable on a stub axle 50 by means of a ballbearing 51 and the stub axle is offset in relation to the shaft axis sothat the latter is tangential to the periphery of the roller 48.

The catch 49 fixed on the mounting plate 47 rides over the template 24when the guide roller 48 rolls along the edge of the template. The endof the template 24 corresponds to the periphery of the lens to be groundand carries a pin 52. When on movement of the tracer head 22 along thetemplate 21 the catch 49 engages the pin 52 the latter acts as a fulcrumto swing the mounting block 47 around the end of template 24 thusimparting a rotating movement to the shaft 40. This shaft in turntransmits its angular movement over the linkage 42, 43, 44-, 45 and 46to the disc 33 and thus to the grinding head 35, which grinds theperiphery of the lens on lens holder 2 corresponding to the curve at theend of template 24.

By appropriate dimensioning the various parts of the pantograph in knownmanner a high ratio of, for example, 40:1 between the movements of thetracer head 22 and the grinding head 35 can be provided, permitting anaccuracy in the grinding of contact lenses not achieved hitherto. Inaddition the required curves can be exactly reproduced as often asrequired.

Although the invention has been described above primarily for thegrinding of secondary curves of contact lenses the same apparatus can beused by proper shaping of the template to grind the required power.Thus, the whole inside of the lens including optic andlimbal bands andthe periphery can be ground in one continuous operation.

In the same way it is also possible to grind the outside or convex sideof a contact lens using a corresponding template.

I claim:

1. In a method of manufacturing from a blank, a concavo-convex contactlens fitting the cornea of a user, said lens having a central optic anda limbal band, the steps of rotating said blank about a fixed axis,grinding the side of said rotating blank which will form the concaveside of said lens to form at least said limbal band, grinding saidrotating blank outside of the limbal band to form the periphery of saidlens, and grinding a portion of the side of said rotating blank whichwill form the convex side of said lens, said last-mentioned portionbeing adjacent said periphery, said grinding steps being performed inthe order recited and in an uninterrupted, continuous and guided manner.

2. In a method of manufacturing from a blank, 21 concavo-convex contactlens fitting the cornea of a user, said lens having a central optic anda limbal band, the steps of rotating said blank about a fixed axis,grinding the side of said rotating blank which will form the concaveside of said lens to form said central optic and said limbal band,grinding said rotating blank-outside of the limbal band to form theperiphery of said lens, and grinding a portion of the side of saidrotating blank which will form the convex side of said lens, saidlast-mentioned portion being adjacent said periphery, said grindingsteps being performed in the order recited and in an uninterrupted,continuous and guided manner.

3. In a method of manufacturing from a blank, a concavo-convex contactlens in accordance with claim 2 which includes the step of polishing theground concave side and the periphery of said rotating blank.

4. The method of manufacturing from a blank, a concavo-convex contactlens in accordance with claim 2 which includes the step of grinding theunground convex portion of the rotating blank in a guided manner to formsaid lens.

References Cited by the Examiner ROBERT C. RIORDON, Primary Examiner.

JOHN C. CHRISTIE, J. SPENCER OVERHOLSER,

LESTER M. SWINGLE, Examiners.

1. IN A METHOD OF MANUFACTURING FROM A BLANK, A CONCAVO-CONVEX CONTACTLENS FITTING THE CORNEA OF A USER, SAID LENS HAVING A CENTRAL OPTIC ANDA LIMBAL BAND, THE STEPS OF ROTATING SAID BLANK ABOUT A FIXED AXIS,GRINDING THE SIDE OF SAID ROTATING BLANK WHICH WILL FORM THE CONCAVESIDE OF SAID LENS TO FORM AT LEAST SAID LIMBAL BAND, GRINDING SAIDROTATING BLANK OUTSIDE OF THE LIMBAL BAND TO FORM THE PERIPHERY OF SAIDLENS, AND GRINDING A PORTION OF THE SIDE OF SAID ROTATING BLANK WHICHWILL FORM THE CONVEX